Method for Designing Mold, Mold and Molded Product

ABSTRACT

On an occasion of molding a molded product from a mold, the mold for molding a molded product in a desired shape can be designed with high precision by correcting a shape change of the molded product.  
     A mold  10  in which use surfaces  16  of an upper mold  11  and a lower mold  12  are formed to be design curved surfaces of an optical lens is prepared. A curved surface shape of the optical lens molded from this mold is measured, and a measured value is approximated by equation (1) which is an equation of an aspherical surface to specify a curved surface of the above-described optical lens as an aspherical surface. The curved surface of the above-described optical lens specified by the equation of the aspherical surface and a design curved surface of the above-described optical lens are compared to obtain an error between both the curved surfaces. Information corresponding to the error is used as correction information (entire shape correction information, local shape correction information), and the use surfaces in the upper mold and the lower mold in the above-described mold are corrected and designed.  
             [     Mathematical   ⁢           ⁢   expression   ⁢           ⁢   14     ]                           Z   =         C   ⁢           ⁢     ρ   2         1   +       1   -       (     1   +   K     )     ⁢     C   2     ⁢     ρ   2               +       ∑     i   =   2     n     ⁢       A     2   ⁢   i       ⁢     ρ     2   ⁢   i                     (   1   )

TECHNICAL FIELD

The present invention relates to a mold designing method for designing amold with which a molded product in a desired shape is molded bycorrecting a shape change of the molded product when molding the moldedproduct (for example, an optical lens) from the mold, a mold designed bythe mold designing method, and a molded product molded by the mold.

BACKGROUND ART

In molding an optical lens, when a mold is designed and produced byusing design values of the optical lens for the mold as they are, theoptical lens produced with the mold sometimes is not produced in thesame shape as that of the design values. This is because of moldshrinkage dependent on the material, stress due to the shape of theoptical lens and the like, and because a mold surface of the mold is nottransferred to a lens surface with high precision.

For example, when molding is performed by using a mold having aspherical molding surface to mold a spherical lens, the molded opticallens sometimes has a surface shape other than a spherical surfaceincluding an aspherical shape. Therefore, in designing a mold, it isnecessary to add a proper shape correction to the mold in considerationof these various factors.

Correction values of the molding surfaces of these molds differ in eachrefractive power of optical lenses, lens material, and shape of thedesign curved surface, and have complicated tendency by combination ofthem. In order to determine a suitable correction value, it is necessaryto experimentally verify the actual deformation in each mold.

Further, prediction and quantification of the correction value aredifficult, and a skill is required in determination of a propercorrection value.

A concrete operation includes: (a) molding all kinds of optical lenseswith the corresponding molds by tests, and (b) measuring errors withrespect to the designing values of the optical lenses; (c) calculatingtemporary correction values (empirical values) by multiplying themeasured errors by various coefficients and remaking the molds; (d)molding optical lenses with the remade molds by tests again, and (e)measuring the shape errors of the optical lenses. It is a general methodto repeat the above-described (c) to (e) to optimize correction.

In order to perform the operation of optimizing such shape correction ofa mold, however, a large number of molding tests are required.Especially in the case of spectacle lenses, various kinds of molds arerequired. Namely, the spectacle lenses, lenses corresponding toprescriptions of the individual spectacle-lenses wearers have to beprepared. For example, when the range of the refractive power at thevertex of a spherical diopter is −8.00 diopter (D) to +6.00 diopter (D),and the division unit of the refractive power is 0.25 D pitch, as forthe diopter range of the spectacle lenses corresponding to theprescriptions, the number of kinds of spherical diopters is 56.

Further, in the case of the cylindrical refractive power correspondingto an astigmatic prescription being in the range of 0.25 diopter (D) to2.00 diopter (D), when the division unit of refractive power is 0.25 Dpitch, eight kinds are required as the kind of astigmatism. Therefore,when the spherical prescription and astigmatic prescription arecombined, it is necessary for a product to prepare for 448 kinds of lensdiopters, and since the mold is composed of two molds that are upper andlower molds, the number of kinds of molds becomes 896 in total.

For this reason, in production of molds, the operation of shapecorrection for each mold as described above is performed, and therefore,a long manufacturing period is required.

Meanwhile, as for a method for making correction which is added to themolding surface of a mold, there is known a method for correcting a moldby obtaining a spherical shape having a single curvature by using theleast squares method so that errors of the molded optical lens and thedesign values of the optical lens become the minimum, and by using thecurvature of the spherical shape as an average curvature (the firstprior art).

Further, as the second prior art, there is a method for applying apredicted value as a correction value when deformation in considerationof shrinkage is predictable in the case of a simple shape (PatentDocument 1).

Further, as the third prior art, there is a method for making correctionbased on a shape error measurement value which is obtained by measuringa three-dimensional shape by an aspherical surface measuring machine,obtaining a shape error from the designing values, and excluding asetting error with respect to the measuring machine from the shape error(Patent Document 2).

[Patent Document 1] Japanese Patent Application Laid-open No.2003-117925

[Patent Document 2] Japanese Patent Application Laid-open No. 8-216272

DISCLOSURE OF THE INVENTION

Problems to be Solved by the Invention

However, in the evaluation of an error by the average curvature in thefirst prior art, shape error other than a spherical shape cannot beevaluated, and therefore, the shape errors of the shapes other than thespherical shapes cannot be corrected.

In the case of designing of the mold of an optical lens by using thesecond prior art, for example, in the case of a spectacle lens, thespectacle lens has a meniscus shape composed of a convex surface and aconcave surface, and the shape is complicated; therefore, it isdifficult to design the mold by predicting a transformation value withshrinkage taken into consideration.

Further, in the third prior art, a measurement error is excluded, butthe shape error measurement value includes influence of roughness of alens surface, foreign matters attached to the lens surface and the likeas noise. Therefore, the noise other than the shape error is reflectedon the correction value, and precision of correction is lowered, thusthere is a possibility of being incapable of molding an optical lensfrom the mold with high precision.

In view of the above-described circumstances, an object of the presentinvention is to provide a mold with which a molded product in a desiredshape is molded by correcting a shape change of the molded product whenthe molded product is molded from the mold, and a method for designingthe mold.

Another object of the present invention is to provide a molded productby using the aforesaid mold.

Means for Solving the Problems

A method for designing a mold according to a first construction ischaracterized by comprising preparing a mold of which molding surface isformed to be a design curved surface of a molded product, measuring acurved surface shape of a molded product which is molded from the mold,and specifying a curved surface of the above-described molded product byapproximating the measured value by an equation of an asphericalsurface, comparing the curved surface of the above-described moldedproduct which is specified by the equation of the aspherical surface andthe design curved surface of the above-described molded product toobtain an error of both the curved surfaces, and correcting theabove-described molding surface of the above-described mold to design itby using information corresponding to the error as correctioninformation.

The method for designing a mold according to a second construction is,in the invention described in the first construction, characterized inthat the above-described correction information includes entire shapecorrection information correcting an entire shape of the molding surfaceof the mold to cope with an error of a spherical shape component in thecurved surface of the molded product, and local shape correctioninformation which corrects a local shape of the above-described moldingsurface of the above-described mold to cope with an error of a componentother than the spherical shape in the curved surface of the moldedproduct.

The method for designing a mold according to a third construction is, inthe invention described in the first or the second construction,characterized in that the above-described equation of the asphericalsurface is a polynomial including a spherical shape component in thecurved surface of the molded product and a component other than thespherical shape in the curved surface of the molded product.

The method for designing a mold according to a fourth construction is,in the invention described in any one of the first to the thirdconstructions, characterized in that the above-described equation of theaspherical surface adds a spherical shape component in the curvedsurface of the molded product and a component other than that of thespherical shape in the curved surface of the molded product.

The method for designing a mold according to a fifth construction is, inthe invention described in any one of the first to the fourthconstructions, characterized in that the above-described equation of theaspherical surface is the following equation (1), where Z is a distancemeasured from a vertex of the molded product in an axial direction ofthe molded product, ρ satisfies ρ²=X²+Y² when X and Y are distancesmeasured in a perpendicular direction to the above-described axis fromthe above-described vertex, a vertex curvature C satisfies C=1/R when Ris the radius of curvature at the vertex, K is a conic coefficient, andA_(2i) is an aspherical coefficient (i is an integer). $\begin{matrix}\lbrack {{Mathematical}\quad{Expression}\quad 1} \rbrack & \quad \\{Z = {\frac{C\quad\rho^{2}}{1 + \sqrt{1 - {( {1 + K} )C^{2}\rho^{2}}}} + {\sum\limits_{i = 2}^{n}{A_{2i}\rho^{2i}}}}} & (1)\end{matrix}$

The method for designing a mold according to a sixth construction is, inthe invention described in the fifth construction, characterized in thatin the above-described aspherical coefficient A_(2i), i is 2 to 5.

The method for designing a mold according to a seventh construction is,in the invention described in the fifth construction, characterized byfurther comprising obtaining the entire shape correction informationcorrecting the entire shape of the molding surface of the mold to copewith the error of the spherical shape component in the curved surface ofthe molded product, according to a reference spherical component whichis a first term (K=0) of the above-described equation (1), and obtainingthe local shape correction information correcting a local shape of theabove-described molding surface of the above-described mold to cope withthe error of a component other than the spherical shape in the curvedsurface of the molded product, according to a polynomial component whichis a second term of the above-described equation (1).

The method for designing a mold according to an eighth construction is,in the invention described in the seventh construction, characterized inthat the entire shape correction information in the molding surface ofthe above-described mold is determined based on a difference between aradius of curvature of a reference spherical surface expressed by thereference spherical surface component which is the first term (K=0) ofthe equation (1) and a radius of curvature in the design curved surfaceof the molded product.

The method for designing a mold according to a ninth construction is, inthe invention described in the seventh or the eighth construction,characterized in that the local shape correction information in themolding surface of the above-described mold is determined based on ashape change rate which is expressed by the polynomial component that isthe second term of the equation (1) and is calculated by using a height(Z value) of a component other than that of the spherical shape in thecurved surface of the molded product, and a height (Z value) of thedesign curved surface of the above-described molded product.

The method for designing a mold according to a tenth construction is, inthe invention described in any one of the seventh to the ninthconstructions, characterized in that design of the molding surface ofthe above-described mold is carried out by adding the entire shapecorrection information and the local shape correction information to thedesign curved surface of the molded product.

The method for designing a mold according to an eleventh constructionis, in the invention described in any one of the first to the tenthconstructions, characterized in that the above-described equation of theaspherical surface is the following equation (2) which is obtained bytransforming the following equation (1). $\begin{matrix}\lbrack {{Mathematical}\quad{expression}\quad 2} \rbrack & \quad \\{Z = {\frac{C\quad\rho^{2}}{1 + \sqrt{1 - {( {1 + K} )C^{2}\rho^{2}}}} + {\sum\limits_{i = 2}^{n}{A_{2i}\rho^{2i}}}}} & (1) \\\lbrack {{Mathematical}\quad{expression}\quad 3} \rbrack & \quad \\{Z = {\sum\limits_{i = 1}^{n}{B_{2i}\rho^{2i}}}} & (2)\end{matrix}$

The method for designing a mold according to a twelfth construction is,in the invention described in the eleventh construction, characterizedby further comprising obtaining the vertex curvature C and an asphericalcoefficient A_(2n) of the equation (1) from a coefficient B_(2n) of theabove-described equation (2) and determining the curved surface of themolded product by the equation (1), obtaining the entire shapecorrection information correcting the entire shape of the moldingsurface of the mold to cope with an error of the spherical shapecomponent in the curved surface of the molded product, according to thereference spherical component which is the first term (K=0) of theequation (1), and obtaining the local shape correction informationcorrecting the local shape of the above-described molding surface of theabove-described mold to cope with the error of a component other thanthe spherical shape in the curved surface of the molded product,according to the polynomial component that is the second term of theabove-described equation (1).

The method for designing a mold according to a thirteenth constructionis, in the invention described in any one of the first to the twelfthconstructions, characterized in that measurement of the curved surfaceshape of the above-described molded product comprises preparing a moldwith a curved surface measuring mark provided on the molding surface,and measuring the curved surface shape of the molded product molded fromthe mold, and on this occasion, measuring the above-described curvedsurface shape with a transfer mark, which is formed by theabove-described mark being transferred onto the curved surface of themolded product and is located at a spot to be measured, as a reference.

The method for designing a mold according to a fourteenth constructionis, in the invention described in the thirteenth construction,characterized in that the above-described transfer mark has a vertextransfer mark part formed at a vertex of the curved surface of themolded product, and edge part transfer mark parts formed at positionswhich are point-symmetrical with respect to the above-described vertexand at edge parts of the above-described curved surface, and measuresthe above-described curved surface of the above-described molded productby passing the vertex transfer mark part and the edge part transfer markparts.

The method for designing a mold according to a fifteenth constructionis, in the invention described in the fourteenth construction,characterized in that a pair of or a plurality of pairs of theabove-described edge part transfer mark parts are formed at positionswhich are point-symmetrical with respect to the vertex of the curvedsurface of the molded product.

The method for designing a mold according to a sixteenth constructionis, in the invention described in any one of the first to the fifteenthconstructions, characterized in that the above-described molded productis an optical lens of which curved surface is in a spherical shape or anaspherical shape.

The mold according to a seventeenth construction is formed by carryingout the method for designing a mold according to any one of the first tothe sixteenth constructions.

The molded product according to an eighteenth construction is formed byusing the mold described in the seventeenth construction.

The molded product according to a nineteenth construction ischaracterized in that the molded product described in the eighteenthconstruction is a spectacle lens in a meniscus shape.

The molded product according to a twentieth construction ischaracterized in that the molded product is a spectacle lens symmetricalwith respect to a center.

ADVANTAGEOUS EFFECT OF THE INVENTION

According to the invention described in any one of the first to thesixth, and the sixteenth constructions, the curved shape of the moldedproduct molded from the mold is measured, and the curved surface of themolded product is specified as the aspherical surface by approximatingthe measured value by the equation of the aspherical surface. Therefore,among the curved surfaces of the molded product, not only the sphericalcomponent but also the components other than the spherical surface canbe quantified and specified by being approximated by the equation of theaspherical surface. Therefore, the error between the curved surface ofthe molded product specified to be the aspherical surface, and thedesign curved surface of the molded product is the error in which thespherical shape component and the component other than the sphericalshape are accurately taken, and the correction information correspondingto the error becomes accurate, thus making it possible to preciselycorrect the molding surface of the mold to design the mold.

Besides, the measured value of the curved surface shape of the moldedproduct is approximated by the equation of the aspherical surface, andthereby the curved shape of the above-described molded product isquantified and specified as the aspherical surface. Therefore, only thesurface shape of the curved surface of the molded product can beextracted by excluding noises such as a measurement error included inthe measured value and surface roughness of the curved surface of themolded product. Therefore, correction of the molding surface of the moldis facilitated and the mold can be designed.

According to the invention described in any one of the seventh to thetenth constructions, the entire shape correction information correctingthe entire shape of the molding surface of the mold is obtained to copewith the error (error of the average surface refractive power) of thespherical shape component in the curved surface of the molded product,according to the reference spherical component of the first term (K=0)of the equation (1). Further, the local shape correction informationcorrecting the local shape of the above-described molding surface of theabove-described mold is obtained to cope with the error of the componentother than the spherical shape in the curved surface of the moldedproduct, according to the polynomial component which is the second termof the above-described equation (1). In this manner, the entire shapecorrection information and the local shape correction information areseparately and independently obtained, whereby the error of the moldedproduct (error of the spherical shape component and the error of thecomponent other than the spherical shape) is precisely reflected in thecorrection information, and suitable correction is made to be able todesign the above-described mold.

According to the invention described in the eleventh or the twelfthconstruction, the curved surface of the above-described molded productis specified by approximating the measured value obtained by measuringthe curved shape of the molded product by the equation (2) that is theequation of the aspherical surface. Accordingly, as compared with thecase where the curved surface of the molded product is specified byusing the equation (1) which is difficult to handle with a calculator,the curved surface can be easily specified, and the coefficient B_(2n)of the equation (2) can be quickly calculated. Therefore, the correctioninformation corresponding to the deformation (error) of the moldedproduct is easily calculated, and the mold for molding the moldedproduct in a desired shape can be easily designed.

According to the invention described in the thirteenth or the fourteenthconstruction, the transfer mark which is formed by transferring the markon the molding surface of the mold onto the curved surface of the moldedproduct is located at the spot which should be measured in the curvedsurface of the molded product. Accordingly, on measuring the curvedsurface shape of the molded product molded from the mold, the curvedsurface shape of the above-described molded product is measured with theabove-described transfer mark as a reference, and thereby, measurementof the curved surface shape of the molded product can be accuratelyconducted. As a result, the measured value is approximated by theequation of the aspherical surface to specify the curved surface of themolded product as the aspherical surface, and the correction informationis calculated, whereby the molding surface of the mold is preciselydesigned and the mold can be designed.

According to the invention described in the fifteenth construction, apair of or a plurality of pairs of edge part transfer marks are formedat a point-symmetrical position with respect to the vertex of the curvedsurface of the molded product. Accordingly, for example, two pairs ofedge part transfer marks can be formed by orthogonalizing the straightlines which respectively connect the two pairs of edge part transfermarks. In this case, when the curved surface shape of the optical lenssuch as a toric lens is measured as a molded product, the curved shapeof the optical lens can be accurately measured in a desired orthogonaldirection with these edge part transfer marks as a reference. As aresult, the mold with which the molded product in a desired shape ismolded can be designed based on the measured value.

According to the invention described in any one of the seventeenth tothe twentieth constructions, even when the molded product is deformedwhen the molded product is molded from the mold, the mold with which themolded product in a desired shape is molded can be designed with highprecision, and therefore, the molded product in the desired shape can bemolded and obtained by this mold.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, best modes for carrying out the present invention will bedescribed based on the drawings.

[A] First Embodiment (FIG. 1 to FIG. 10)

FIG. 1 is a sectional side view showing a mold having an upper mold anda lower mold which are produced by carrying out the first embodiment ina method for designing a mold according to the present invention. FIG. 5is a graph showing a molded curved surface, a design curved surface andthe like of an optical lens which is a molded product molded by testsfrom the mold in FIG. 1. FIG. 7 is a schematic diagram showingcalculation or the like of entire shape correction information and localshape correction information in the design process of the upper mold andthe lower mold in FIG. 1.

(Explanation of Construction of Molding Mold for Producing Lens)

A mold 10 shown in FIG. 1 is for molding a plastic spherical lens by amanufacturing method called a cast method, and is constructed byincluding an upper mold 11, a lower mold 12 and a gasket 13. Theabove-described upper mold 11 and the lower mold 12 are collectivelycalled a lens base mold.

The gasket 13 is formed of a resin having elasticity into a cylindricalshape, and holds the upper mold 11 and the lower mold 12 fluid-tightlyat an inner peripheral surface to be spaced at a predetermined distance.A cavity 14 is constructed by being enclosed by the upper mold 11, thelower mold 12 and the gasket 13. The gasket 13 is integrally providedwith an injection part 15 for injecting a monomer, which is a rawmaterial of an optical lens into the cavity 14. A height of the gasket13 is set at such a dimension as can ensure a thickness of a peripheraledge portion of the optical lens that is a molded product.

The upper mold 11 and the lower mold 12 are composed of glass or thelike. The upper mold 11 is formed into a concave mold to form a curvedsurface (convex surface) of the optical lens. The lower mold 12 isformed into a convex mold to form a curved surface (concave surface) ofthe optical lens. In the upper mold 11 and the lower mold 12, a surfaceon which a lens curved surface of the optical lens is formed is called ause surface 16 and a surface on which the above-described lens curvedsurface is not formed is called a nonuse surface 17 as also shown inFIG. 2.

(Description of Method for Producing Optical Lens)

A manufacturing process of an optical lens using the above-describedmold 10 will be described with reference to FIG. 3.

First, a monomer that is a raw material of the optical lens is prepared(S1). The monomer is a thermosetting resin, and a catalyst, anultraviolet absorber and the like are added to the resin to be prepared,which is filtered with a filter (S2).

Next, the upper mold 11 and the lower mold 12 is assembled to the gasket13 to complete the mold 10 (S3). Then, the monomer prepared as describedabove is injected into the cavity 14 of the mold 10, and isheat-polymerized and cured in an electric furnace (S4). As thepolymerization of the monomer in the mold 10 is completed, the plasticoptical lens is molded, and the optical lens is released from the mold10 (S5).

After the release of the optical lens, heating treatment called annealis carried out to remove distortion of an inside of the lens which iscaused by polymerization (S6). Thereafter, visual inspection andprojective inspection are carried out for the optical lens asintermediate inspection.

The optical lens is classified into a finished product and asemi-finished product (semi product) at this stage, and polishing of asecond surface is performed for the semi-finished product in accordancewith the prescription. For the finished product, a coloring process forobtaining a colored product, a reinforcement coating process forreinforcement against a damage, and an antireflection coating processfor prevention of reflection are carried out thereafter (S7), and finalinspection is carried out (S8). The finished product becomes a productafter the final inspection (S9).

A manufacturing procedure of the upper mold 11 and the lower mold 12 ofthe mold 10 used in the above-described manufacturing process of theoptical lens will be described next with reference to FIG. 4.

The upper mold 11 and the lower mold 12 are obtained by processing bothsurfaces of pressed thick glass blanks, and therefore, the glass blanksare prepared first (S11).

By processing each of the glass blanks, a surface imperfection layer ona press surface of the glass blank is removed, and the use surface 16and the nonuse surface 17 are made to have radiuses of curvature withpredetermined precision and at the same time, the use surface 16 and thenonuse surface 17 with microscopic and uniform roughness with highprecision are obtained. The above-described work of the glass blanks iscarried out by grinding and polishing.

In a grinding process, more specifically, a diamond wheel is used in afree curved surface grinding machine which performs an NC control, andboth surfaces of the glass blanks (use surface 16 and the nonuse surface17) are ground to predetermined radiuses of curvature (S12). By thegrinding process, the upper mold 11 and the lower mold 12 are formedfrom the glass blanks.

In a polishing process, a polishing plate made by attaching polyurethaneor felt onto a hollow plate of rubber is used, and with fine particle ofcerium oxide/zirconium oxide or the like as an abrasive, both surfacesof the upper mold 11 an the lower mold 12 formed by grinding arepolished (S13). By the polishing process, asperities on the surfaces inthe use surfaces 16 and the non use surfaces 17 of the upper mold 11 andthe lower mold 12, which occur in the grinding process, are removed toachieve transparency (graining removal). Then, the use surfaces 16 andthe nonuse surfaces 17 are effectively finished to have sufficientsurface precision.

After the polishing process, the upper mold 11 and the lower mold 12 areinspected (S14), and a hidden mark which is a reference position of alayout pattern is marked on each of the use surfaces 16 (S15). Thelayout pattern indicates an optical layout of the optical lens, and isused when a circular optical lens is framed into a spectacle glassframe. The layout pattern is erasably marked on the surface of theoptical lens.

After marking the hidden mark, scientific glass reinforcement treatmentis carried out for the upper mold 11 and the lower mold 12 (S16), andthe upper mold 11 and the lower mold 12 are completed (S17). The uppermold 11 and the lower mold 12 are produced in accordance with therefractive power of the prescription of the optical lens, and therefore,many kinds of the upper molds 11 and the lower molds 12 as well as thegaskets 13 are required.

(Description of Method for Designing Mold)

A designing procedure of the upper mold 11 and the lower mold 12 in themold 10, which are produced as described above, will be described nextwith reference to FIG. 5 and FIG. 7.

First, the mold 10 with which the optical lens being a molded product ismolded by tests is prepared. The above-described optical lens to bemolded is a spherical lens of which curved surface is a spherical curvedsurface. Accordingly, the use surfaces 16 which are the molding surfacesin the upper mold 11 and the lower mold 12 of the mold 10 are alsoformed into spherical shapes. In this case, a radius of curvature of theuse surface 16 of each of the upper mold 11 and the lower mold 12 isformed to be equal to a set value of the curved surface of the opticallens (for example, a design radius of curvature R₀ at the vertex as aradius of curvature at the vertex power of the lens). Note that thecurved surface of the optical lens having the design radius of curvatureR₀ at the vertex is called a design curved surface 20 (FIG. 5).

Next, a molding test is carried out by using the mold 10 including theabove-described upper mold 11 and the lower mold 12, a monomer isinjected into the mold 10 and is heat-polymerized, and thereby, theoptical lens which is a test molded product is molded. The curvedsurface shape of the optical lens molded by tests is not formed into aspherical shape due to thermal shrinkage of the monomer, and the like.The inventor of the present invention has found out that the majorconstituent of an error due to shape change after molding can beapproximated by the equation of the aspherical surface expressed by thefollowing expression (1) as a result of the earnest study. Namely, thecurved surface shape of the optical lens formed by tests is molded intothe shape other than a spherical shape, which includes an asphericalshape. Thus, the curved surface shape of the surface of the optical lensthus molded is measured by using the shape measuring machine with alater-described transfer marking 32 (FIG. 9) as a reference (S21 in FIG.7). Then, the measured value is approximated by the equation of theaspherical surface by using the least square method, and the curvedsurface of the optical lens molded by tests is quantified and specifiedas an aspherical surface.

The above-described equation of the aspherical surface is the followingequation (1) expressing the aspherical shape of rotational symmetry,where Z is a distance measured from a vertex O in the direction of anoptical axis P, ρ satisfies ρ²=X²+Y² when X and Y are distances measuredfrom the above-described vertex O in a direction perpendicular to theabove-described optical axis P, a vertex curvature C satisfies C=1/Rwhen R is the radius of curvature at the vertex, K is a coniccoefficient, and A_(2i) is an aspherical coefficient (i is an integer).The equation (1) is also called the equation of Spencer. $\begin{matrix}\lbrack {{Mathematical}\quad{Expression}\quad 4} \rbrack & \quad \\{Z = {\frac{C\quad\rho^{2}}{1 + \sqrt{1 - {( {1 + K} )C^{2}\rho^{2}}}} + {\sum\limits_{i = 2}^{n}{A_{2i}\rho^{2i}}}}} & (1)\end{matrix}$

However, in reality, in order to facilitate the calculation, by usingthe following equation (2) which is the result of transforming theabove-described equation (1), the above-described measured value isapproximated by the equation (2) by using the least square method, andquantified and specified, and a coefficient B_(2i) (coefficientincluding the vertex curvature C and the aspherical coefficient A_(2i)of the equation (1)) of the equation (2) is calculated. Here, i of thecoefficient B_(2i) is an integer. $\begin{matrix}\lbrack {{Mathematical}\quad{Expression}\quad 5} \rbrack & \quad \\{Z = {\sum\limits_{i = 1}^{n}{B_{2i}\rho^{2i}}}} & (2)\end{matrix}$

Transformation from the equation (1) to the equation (2) is performed asfollows. Namely, when the first term of the equation (1) is rationalizedwith Q=1+K (K is a conic coefficient), $\begin{matrix}{\lbrack {{Mathematical}\quad{Expression}\quad 6} \rbrack\quad} & \quad \\{{{FIRST}\quad{TERM}\quad{OF}\quad{THE}\quad{EQUATION}\quad(1)} = \frac{1 - \sqrt{1 - {{QC}^{2}\rho^{2}}}}{QC}} & (a)\end{matrix}$When the part of the square root is series-expanded, $\begin{matrix}\lbrack {{Mathematical}\quad{Expression}\quad 7} \rbrack & \quad \\{\sqrt{1 - {{QC}^{2}\rho^{2}}} = {1 - \frac{{QC}^{2}\rho^{2}}{2} - \frac{Q^{2}C^{4}\rho^{4}}{8} - \frac{Q^{3}C^{6}\rho^{6}}{16} - \frac{5Q^{4}C^{8}\rho^{8}}{128} - \frac{7Q^{5}C^{10}\rho^{10}}{256} - \ldots}} & \quad\end{matrix}$When this is substituted into the equation (a), $\begin{matrix}\lbrack {{Mathematical}\quad{Expression}\quad 8} \rbrack & \quad \\{{{FIRST}\quad{TERM}\quad{OF}\quad{THE}\quad{EQUATION}\quad(1)} = {\frac{C\quad\rho^{2}}{2} + \frac{{QC}^{3}\rho^{4}}{8} + \frac{Q^{2}C^{5}\rho^{6}}{16} + \frac{5Q^{3}C^{7}\rho^{8}}{128} + \frac{7Q^{4}C^{9}\rho^{10}}{256} + \ldots}} & \quad\end{matrix}$When this is substituted into the equation (1) and is arranged as thepolynomial equation of ρ, the above-described equation (1) can beexpressed by the following equation (2). $\begin{matrix}\lbrack {{Mathematical}\quad{Expression}\quad 9} \rbrack & \quad \\\begin{matrix}{Z = {{( \frac{C}{2} )\rho^{2}} + {( {\frac{{QC}^{3}}{8} + A_{4}} )\rho^{4}} + ( {\frac{Q^{2}C^{5}}{16} + A_{6}} )}} \\{\rho^{6} + {( {\frac{5Q^{3}C^{7}}{128} + A_{8}} )\rho^{8}} + \ldots} \\{= {\sum\limits_{i = 1}^{n}{B_{2i}\rho^{2i}}}}\end{matrix} & (2)\end{matrix}$Note that $\begin{matrix}\lbrack {{Mathematical}\quad{Expression}\quad 10} \rbrack & \quad \\{{B_{2} = ( \frac{C}{2} )},{B_{4} = ( {\frac{{QC}^{3}}{8} + A_{4}} )},{B_{\quad 6} = ( {\frac{\quad{Q^{\quad 2}\quad C^{\quad 5}}}{\quad 16} + A_{\quad 6}} )},{B_{\quad 8} = ( {\frac{5\quad Q^{\quad 3}\quad C^{\quad 7}}{\quad 128} + A_{\quad 8}} )},\ldots} & (b)\end{matrix}$

As described above, from the coefficient B_(2i) which is calculated byapproximating the measured value of the curved surface shape of theoptical lens molded by tests by the equation (2), the vertex curvature Cand the aspherical coefficient A_(2i) of the equation (1) are calculatedby using the above-described equation (b). Thereby, the curved surfaceshape of the optical lens molded by tests is quantified by the equation(1) and specified. However, the measurement value of the curved surfaceshape of the optical lens molded by tests may be directly approximatedby the equation (1) and quantified to be specified, and the vertexcurvature C and the aspherical coefficient A_(2i) of the equation (1)may be obtained. In any case, on quantification by the equation (1), theconic coefficient K is set at K=0 (namely, Q=1), and the vertexcurvature C is calculated with the first term of the equation (1) usedas the equation which expresses the spherical surface, then theaspherical coefficients A₄, A₆, A₈ and A₁₀ are calculated with i=2, 3, 4and 5.

The curved surface shape of the optical lens molded by tests, which isspecified by the equation (1) is shown as a molded curved surface 21 inFIG. 5. The molded curved surface 21 is in the aspherical shape.Reference numeral 22 in FIG. 5 shows a curved surface shape of areference spherical component which is the first term (K=0) of theequation (1) of the molded curved surface 21 of the optical lens, whichis quantified and specified by the equation (1). The curved surfaceshape 22 shows the spherical surface (reference spherical surface) withthe radius of curvature R at the vertex (R=1/C) which is the inversenumber of the vertex curvature C of the equation (1) as the radius ofcurvature.

Further, ZN in FIG. 5 represents a component other than the sphericalshape of the molded curved surface 21 of the optical lens quantified andspecified by the equation (1), and shows the polynomial component thatis the second term of the equation (1). The above-described polynomialcomponent represented by the ZN is an error component with respect tothe reference spherical component of the first term of the equation (1)as expressed by reference numeral 23 in FIG. 6.

Next, data of the optical lens which is molded by tests and quantifiedand specified by the equation (1) is analyzed (S22 in FIG. 7). In thisdata analysis, the vertex curvature C (radius of curvature R at thevertex) of the equation (1) and the aspherical coefficients A₄, A₆, A₈and A₁₀ are used. For example, when the design radius of curvature R₀ atthe vertex of the design curved surface 20 of the optical lens is set atR₀=532.680 mm, the radius of curvature R at the vertex (=1/C) of themolded curved surface 21 of the optical lens which is molded from themold 10 having the upper mold 11 and the lower mold 12 each with the usesurface 16 formed to be the above-described design curved surface 20,and is quantified and specified by the equation (1) is set at R=489.001mm, and the aspherical coefficients A₄, A₆, A₈ and A₁₀ are set as shownin Table 1. The radius of curvature R at the vertex and the asphericalcoefficients A₄, A₆, A₈ and A₁₀ are used in the data analysis. TABLE 1ASPHERICAL ASPHERICAL i COEFFICIENT COEFFICIENT VALUE 2 A₄  1.35749160310267 × 10⁻⁷ 3 A₆ −5.09568302053733 × 10⁻¹¹ 4 A₈−3.82812002603438 × 10⁻¹⁵ 5 A₁₀    3.9996422621367 × 10⁻¹⁸

(Mold Designing Method: Separation of Spherical and AsphericalComponents of Error)

In this data analysis, the reference spherical component which is thefirst term of the equation (1) by which the optical lens molded by testsis quantified and specified, and the polynomial component which is thesecond term of the equation (1) are dealt separately and independently.

Incidentally, in the prior art, the spherical component and theaspherical component of a shape error are integrally corrected.Accordingly, as for the correction coefficient of the shape error, thesame coefficient is applied to the spherical component and theaspherical component. However, the correction numeric value of each lensshape which will be described later totally differs for each shape inthe spherical component and the aspherical component of a shape error.For example, FIG. 12(b) shows a correction numeric value in the concavesurface side of the spherical component of the shape error. FIG. 12(b)shows that even if the surface shape of the lens changes, the sphericalcomponent correction value on the concave surface side is constantexcept for some shapes. Further, FIG. 12(a) shows the correction numericvalue on the convex surface side of the spherical component of the shapeerror. The correction numeric value shown in FIG. 12(a) indicates thatthe shape of the convex side becomes constant at the refractive power of4D or more. Namely, as for the entire shape correction value, thecorrection numeric values of the shape errors are constant on bothconcave and convex surfaces at the refractive power of 4D or more.Namely, as for the entire shape correction value, the correction numericvalues of the shape errors are constant on both the concave and convexsurfaces at the refractive power of 4D or more. On the other hand, theaspherical component of the shape error shows a different value at eachrefractive power, and there is no tendency in the shape error and thecorrection value, and the shape of the molded product.

However, in the prior art, the spherical component and the asphericalcomponent of a shape error are integrally corrected. Accordingly, thecorrection values are changed in all the shapes. However, correction ismade by changing the correction values for the shape error sphericalcomponents of the lens shape at the refractive power of 4D or more forwhich the correction value does not have to be changed originally, andtherefore, determination of the correction values is furthercomplicated. As a result, suitable correction values are determined bysufficiently repeating trial manufacture for each of all the molds. Inthis embodiment, the spherical component and the aspherical component ofa shape error are separated, and correction information is obtainedindependently, whereby proper correction is carried out and the mold canbe easily designed.

Namely, information, which corresponds to an error of the sphericalcomponent among errors between the molded curved surface 21 (FIG. 5) ofthe optical lens molded by tests and quantified and specified by theequation (1) and the design curved surface 20 of the optical lens, iscalculated by using the reference spherical component (shape expressedby the curved surface shape 22 in FIG. 5) that is the first term (K=0)of the equation (1). The information is set as entire shape correctioninformation (S23 in FIG. 7). The entire shape correction information isfor correcting the entire surface shape of the use surfaces 16 in theupper mold 11 and the lower mold 12 of the mold 10 and for eliminatingthe error of the above-described spherical shape component.

More specifically, a difference H in a Z-direction between the radius ofcurvature R at the vertex of the curved shape 22 (reference sphericalsurface) expressed by the reference spherical component that is thefirst term (K=0) of the equation (1) which quantifies and specifies themolded optical lens, and the design radius of curvature R₀ at the vertexin the design curved surface 20 of the optical lens is calculated as anerror of the spherical shape component in the molded curved surface 21of the molded optical lens. The difference H is determined as the entireshape correction information. The entire shape correction information isnecessary correction information for the molded optical lens to obtaindesired refractive power.

The radius of curvature R at the vertex of the curved surface shape 22(reference spherical surface) expressed by the reference sphericalcomponent that is the first term (K=0) of the equation (1) whichquantifies and specifies the molded optical lens, and the design radiusof curvature R₀ at the vertex in the design curved surface 20 of theoptical lens sometimes do not correspond with each other due to the rateof shrinkage of a raw material. The rate of shrinkage differs in eachraw material. When the difference between the radius of curvature R atthe vertex and the design radius of curvature R₀ at the vertex is 2D orless, preferably 1D or less, in surface refraction power conversion of alater-described equation (3), the molded curved surface of the moldedproduct (optical lens) can be formed into a desired shape by using theabove-described entire shape correction information and thelater-described local shape correction information.

Further, information, which corresponds to an error of the componentsother than the spherical shape among errors between the molded curvedsurface 21 of the optical lens molded by tests and quantified andspecified by the equation (1) and the design curved surface 20 of theoptical lens, is calculated by using the polynomial component (expressedby ZN in FIG. 5) which is the second term of the equation (1). Theinformation is set as the local shape correction information. (S24 inFIG. 7). The local shape correction information is for correcting thelocal shape of the use surfaces 16 in the upper mold 11 and the lowermold 12 of the mold 10, namely, partially correcting the use surfaces 16and eliminating errors of the components other than the above-describedspherical shape.

More specifically, a shape change rate is calculated by using a height(Z value) ZN of the component other than the spherical shape in themolded curved surface 21 (FIG. 5) of the optical lens, which isexpressed by the polynomial component that is the second term of theequation (1) quantifying and specifying the molded optical lens, and aheight (Z value) ZM in the design curved surface 20 of the optical lens.The shape change rate is calculated with the shape change rate=ZN/ZM,and is calculated at each position from the vertex of the optical lensmolded by tests. The local shape correction information is calculatedand determined in each position from the vertex of the optical lensmolded by tests as the value obtained by multiplying the shape changerate in the position by the height ZM of the design curved surface 20 ofthe optical lens at the position.

Here, the above-described height ZN is expressed by the difference ofthe respective heights (Z values) at the same position from the vertexof the optical lens in the curved surface shape 22 (reference sphericalsurface) expressed by the reference spherical component of the firstterm (K=0) of the equation (1) and the molded curved surface 21 of theoptical lens molded and specified by the equation (1).

Finally, the use surfaces 16 of the upper mold 11 and the lower mold 12in the mold 10 are corrected and designed by using the local shapecorrection information and the entire shape correction informationcalculated as described above (S25 in FIG. 7).

Namely, the local shape correction information corresponding to eachposition is first added in the Z-direction to the design value of eachposition from the vertex of the lens in the use surfaces 16 of the uppermold 11 and the lower mold 12 formed to be the design curved surface 20of the optical lens. Thereby, the errors of the components other thanthe spherical shape in the molded curved surface 21 of the optical lensto be molded are eliminated. Next, the entire shape correctioninformation (difference H) is added in the Z-direction to the designvalues of the entire surfaces in the use surfaces 16 of the upper mold11 and the lower mold 12 to which the local shape correction informationis added. Thereby, the errors of the spherical components in the moldedcurved surface 21 of the optical lens to be molded are eliminated. Inthis manner, the design values of the use surfaces 16 of the upper mold11 and the lower mold 12 are corrected, and the use surfaces 16 aredesigned.

Addition of the above-described entire shape correction information maybe carried out only for the design value of the use surface 16 of thelower mold 12. The reason is that the lower mold 12 is common in variouskinds of optical lenses, and has less the number of use surfaces 16 tobe corrected than the upper mold 11 does. Besides, the reason is thatthe influence is considered to uniformly act on the curved surface(convex surface) of the optical lens by changing the radius of curvatureof the curved surface (concave surface) of the optical lens molded bythe use surface 16 of the lower mold 12.

A design procedure for correcting and designing the use surfaces 16 ofthe upper mold 11 and the lower mold 12 as described above will befurther described with reference to FIG. 8.

The use surfaces 16 of the upper mold 11 and the lower mold 12 have tobe larger than the size of the optical lens to be molded, and therefore,the design values of the use surfaces 16 are calculated by increasingthe design values of the curved surfaces of the optical lens (S31).Based on the calculated design values, the upper mold 11 and the lowermold 12 are produced so that the use surfaces 16 become equal to thedesign curved surfaces of the optical lens (design radius of curvatureR₀ at the vertex), and the mold 10 is assembled (S32).

Next, a monomer is injected into the assembled mold 10, the optical lensis molded by tests, and the curved surface shape of the optical lensbeing the molded product is measured by using a shape measuring devicewith a later-described transfer marking 32 (FIG. 9) as a reference(S33). As the shape measuring device, for example, Form Talysurf made byTaylor Hobson Ltd. is mainly used in this embodiment, but a non-contacttype three-dimensional measuring device (for example, UA3P made byMatsushita Electric Industrial Co., Ltd., and the like) and the like canbe used, and the measuring device is not especially limited. In FormTalysurf, ruby or diamond is set at a tip end of a probe, the tip end ofthe probe moves on the surface of a lens in contact with the surface andscans the lens surface to measure the surface shape, and its measuringlocus is usually only a straight line. Meanwhile, the three-dimensionalmeasuring device is a type of floating from a measured surface by anintermolecular force by a very small constant amount.

Next, the above-described measurement value of the optical lens moldedby tests is approximated by using the least square method in theequation (2), then the curved surface shape of the molded optical lensis quantified and specified, and the coefficient B_(2i) is calculated.Further, from the coefficient B_(2i), by using the equation (b), thevertex curvature C of the equation (1) (K=0) and the asphericcoefficients A₄, A₆, A₈ and A₁₀ are calculated, and the curved surfaceshape of the molded optical lens is quantified and specified by theequation (1) (K=0).

Thereafter, by using the above-described vertex curvature C andaspherical coefficients A₄, A₆, A₈ and A₁₀, data of the optical lensmolded and quantified by the equation (1) is analyzed (S34). In thiscase, the first term (K=0) and the second term of the equation (1) aretreated separately and independently, the entire shape correctioninformation is calculated from the first term (K=0) (S35), and the localshape correction information is calculated from the second term. (S36).

Next, the calculated local shape correction information and entire shapecorrection information are added to the design values of the respectiveuse surfaces 16 of the upper mold 11 and the lower mold 12 which areformed to be the design curved surface (design radius of curvature R₀ atthe vertex) of the optical lens, and the use surfaces 16 are correctedand designed (S37).

Next, design of the nonuse surfaces 17 of the upper mold 11 and thelower mold 12 is carried out (S38). Then, data for processing machine iscreated from the design values of the use surfaces 16 and the nonusesurfaces 17 in the upper mold 11 and the lower mold 12 (S39).Thereafter, glass blanks are selected, and the upper mold 11 and thelower mold 12 of the mold 10 are produced by a grinding machine and apolishing machine (S40).

(Comparison of Molded Product Precision of Embodiment and Prior Art)

The shape precision of the molded product according to this embodimentwill be described.

The optical lens molded by the mold 10 having the upper mold 11 and thelower mold 12 which are produced as described above has the curvedsurfaces in desired spherical: shapes. For example, FIG. 10(A) is ashape error measurement result when the curved surface of the moldedproduct according to this embodiment is measured in the differentdiameter directions (two orthogonal directions to each other in thedrawing). FIG. 10(B) is a shape error measurement result when the curvedsurface of the molded product according to the above-described firstprior art is measured in the different diameter directions (twoorthogonal directions to each other in the drawing). FIG. 10A and FIG.10B are the measurement results of the molded products which are opticallenses with the surface refraction power of 5.00 D (diopter) molded bythe mold 10. In FIG. 10, the horizontal axis represents a distance (mm)from a lens center (vertex), and 0 at the central part of the graphrepresents an optical lens center. The vertical axis represents arefractive power error amount, and 0.00 D indicates no error. Based onFIG. 10, shape error amounts of the molded products molded according tothis embodiment and the first prior art will be described in detail.

A lens central part will be explained first. The lens central part isfrequently used and is especially important as the optical center. Theerror amounts at the optical lens central parts obviously differ, andthe error amount is 0.06 D in this embodiment (FIG. 10(A)) while in thefirst prior art (FIG. 10(B)), the error amount is 0.18 D. Accordingly,it is understood that the precision is enhanced by three times in thisembodiment as compared with the above-described prior art.

Further, a peripheral part other than the lens central part will beexplained. In this peripheral part, the shape error with respect to thedesign curved surface of the optical lens when the curved surface of themolded optical lens is measured in the different diameter directions(two directions orthogonal to each other in the drawing) is small in themolded product according to this embodiment in any position of each partof the lens. When comparing the shape errors in the vicinity of theouter diameter of 50 mm of the spectacle lens used in a generalspectacle frame, the error amount is about 0.02 D in this embodiment,while in the first prior art, the error amount is 0.04 D. Accordingly,it is found out that precision in this embodiment is enhanced abouttwice as high as the one in the above-described prior art.

Further, as for the error amount of this embodiment, the change amountof the error is small and gentle from the lens central part to theperipheral part as compared with the first prior art. Therefore, thereis the effect of having less incompatibility even if the visual lineposition moves from the central part to the peripheral part by rotationof an eye.

From these results, it is found out that the optical lens molded in themold 10 according to the designing method of this embodiment is in thesubstantially equal shape to the design curved surface. Besides, it isdetermined that the optical lens molded by the mold in the first priorart is in the shape different from the design curved surface.

Here, each of the vertical axes in FIGS. 10(A) and 10(B) represents therefractive power error (unit: D (diopter)). The refractive power erroris the error of the radius of curvature r (unit: m) indicating thecurved shape of the optical lens, which is converted into the error ofthe surface refractive power P (unit: D (diopter)) of theabove-described curved surface of the optical lens by the followingequation (3).P=(n−1)/r   (3)In this equation (3), n represents a refractive index of the opticallens. Note that in the optical lens in the meniscus shape having theconvex surface and the concave surface, the sum of the surfacerefractive powers of the convex surface and the concave surfaceexpresses the refractive power of the optical lens.

(Explanation of Surface Shape Measurement)

Next, the transfer mark 32 (FIG. 9(A)) set as a reference when thecurved shape of the optical lens molded by tests in step 21 in FIG. 7and step 33 in FIG. 8 will be described. The transfer mark 32 is formedby transferring marks (not shown) formed on the use surfaces 16 of theupper mold 11 and the lower mold 12 of the mold onto the curved surface31 of the optical lens 30 which is molded by tests.

Further, as is understood from the FIGS. 9(B) and 9(C), the transfermark 32 has a vertex transfer mark part 33 which is formed on theportion of the vertex O in the curved surface 31 of the optical lens 30,and a pair of peripheral edge part transfer mark parts 34A and 34Bformed at positions which are on the peripheral edge part of theabove-described curved surface 31 and symmetrical with respect to theabove-described vertex O. Further, the above-described vertex transfermark part 33 has a main vertex transfer mark part 35 which is formed atthe vertex O of the curved surface 31, and sub vertex transfer markparts 36 which radiate out at predetermined distances from the mainvertex transfer mark part 35 and are formed to be orthogonal to eachother.

For example, the main vertex transfer mark part 35 is a circular convexpart with the diameter of about 0.5 mm. Further, the peripheral edgepart transfer mark parts 34A and 34B are circular convex parts each witha diameter of about 1 mm. Further, the sub vertex transfer mark part 36is a rectangular convex part with the length S of about 2 mm, a spaceddistance T between the sub vertex transfer mark parts 36 on the samestraight line of about 1 mm, and width dimension of the sub vertextransfer mark part 36 of several tens μm.

On each of the use surfaces 16 of the upper mold 11 and the lower mold12, markings (not shown) in concave shapes in the corresponding sizesare formed at the positions corresponding to the above-described mainvertex transfer mark part 35, the sub vertex transfer mark parts 36, andthe peripheral edge part transfer mark parts 34A and 34B. Thereby, theabove-described vertex transfer mark 33 (the main vertex transfer markpart 35, the sub vertex transfer mark parts 36), the peripheral parttransfer mark parts 34A and 34B are transferred and formed on the curvedsurface 31 of the optical lens 30. The markings for transferring theperipheral part transfer mark parts 34A and 34B are cut to be about 1 mmin diameter and several μm in depth. The marking for transferring themain vertex transfer mark part 35 is cut to be about 0.5 mm in diameterand about 0.5 μm or less in depth. The marking for transferring the subvertex transfer mark part 36 is formed by being scribed to be severaltens μm in width and several μm or less in depth.

The vertex transfer mark part 33 (especially the main vertex transfermark part 35), and the peripheral edge part transfer mark parts 34A and34B, which are transferred to be formed on the curved surface 31 of theoptical lens 30, are on the same straight line L1 passing the vertex Oof the curved surface 31. The shape measuring device which measures theshape of the curved surface 31 of the optical lens 30 measures the shapeof the above-described curved surface 31 by sequentially passing theperipheral part transfer mark part 34A, the vertex transfer mark part 33and the peripheral part transfer mark part 34B along the above-describedstraight line L1, and thereby the shape measuring device is capable ofaccurately measuring the shape of the curved surface 31. Accordingly,the vertex transfer mark part 33 (especially, the main vertex transfermark part 35), and the peripheral edge part transfer mark parts 34A and34B are located at the spot where the curved surface 31 of the opticallens 30 should be measured.

When the shape measuring device measures the curved surface 31 of theoptical lens 30 by sequentially passing the peripheral edge parttransfer mark part 34A, the vertex transfer mark part 33 and theperipheral edge part transfer mark part 34B along the straight line L1,the vertex transfer mark part 33, the peripheral edge part transfer markparts 34A and 34B have an extreme shape change, and therefore, it ismeasured as a large noise. Therefore, when the noise of the vertextransfer mark part 33, the peripheral edge part transfer mark parts 34Aand 34B is not measured, it is obvious that the shape measurement in thecurved surface 31 of the optical lens 30 by the shape measuring deviceis not accurately conducted. In this case, setting of the optical lens30 with respect to the shape measuring device is adjusted, so that theshape measuring device performs measurement by sequentially passing theperipheral edge part transfer mark part 34A, the vertex transfer markpart 33 and the peripheral edge part transfer mark part 34B.

Note that the large noise in the above-described measured value causedby the vertex transfer mark part 33, and the peripheral edge parttransfer mark parts 34A and 34B can be easily excluded without having aninfluence on the measured values nearby. Thereafter, the above-describedmeasured value is approximated by the equation (1) of the asphericalsurface or the equation (2) by using the least square method asdescribed above, and therefore, no influence is on the measured value.As for the measurement error of the vertex transfer mark part 33, andthe peripheral edge part transfer mark parts 34A and 34B, themeasurement error for the peripheral edge part transfer mark parts 34Aand 34B is within about 0.5 mm because the peripheral edge part transfermark parts 34A and 34B are each in a circular shape of about 1 mm indiameter. The measurement error for the main vertex transfer mark part35 is within about 0.25 mm because the main vertex transfer mark part 35of the vertex transfer mark part 33 is in a circular shape of about 0.5mm in diameter.

The present invention is not limited to the case where a set ofperipheral edge transfer mark parts 34A and 34B are provided to besymmetric with respect to the vertex O in the curved surface 31 of theoptical lens 30, but a plurality of peripheral edge transfer mark parts34A and 34B may be provided. For example, another set of peripheral edgepart transfer mark parts 34A and 34B may be transferred on a straightline L2, which is rotated at a predetermined angle (for example, 90degrees) with respect to the straight line L1 including the peripheraledge part transfer mark parts 34A and 34B as well as the peripheral parttransfer mark parts 34A and 34B on the straight line L1. The shapemeasuring device measures the curved surface 31 of the optical lens 30in the different diameter directions along the above-described straightlines L1 and L2, and thereby, it becomes possible to accurately measurethe curved surface 31 of the optical lens 30 such as a toric lens, forexample, in both the orthogonal axial directions.

The transfer mark 32 is further provided in an optional direction in thecurved surface 31 of the optical lens 30, and in this direction, thecurved surface shape of the curved surface 31 may be measured in thisdirection by the shape measuring device.

(Effect of the First Embodiment)

Since the first embodiment is constructed as above, the followingeffects (1) to (5) are provided according to the above-describedembodiment.

(1) The curved surface shape of the optical lens which is molded fromthe mold 10 including the upper mold 11 and the lower mold 12 ismeasured, and the measured value is approximated by the equation (1)that is the equation of the aspherical surface and the curved surface ofthe optical lens is specified as the aspherical surface. Therefore, ofthe curved surface shape of the molded optical lens, not only thespherical components but also the components other than the sphericalcomponents can be approximated by the equation (1) of the asphericalsurface, and quantified and specified. Accordingly, the error betweenthe curved surface of the optical lens specified to be the asphericalsurface and the design curved surface of the optical lens becomes theerror in which the spherical shape components and the components of theshape other than the spherical shape are accurately taken. As a result,the correction information corresponding to the above-described errorbecomes accurate, the upper mold 11 and the lower mold 12 can bedesigned by precisely correcting the use surfaces 16 of the upper mold11 and the lower mold 12 in the mold 10.

(2) The measured value of the curved surface shape of the molded opticallens is approximated by the equation (1) which is the equation of theaspherical surface, and the curved shape of the above-described opticallens is quantified and specified as the aspherical surface. Accordingly,the measurement error included in the measured value and a noise such assurface roughness of the curved surface of the optical lens can beexcluded, and only the measured value of the curved surface of theoptical lens can be extracted. Therefore, the upper mold 11 and thelower mold 12 can be designed by precisely carrying out the correctionof the use surfaces 16 of the upper mold 11 and the lower mold 12 in themold 10.

(3) Based on the reference spherical component which is the first term(K=0) of the equation (1), the entire shape correction information forcorrecting the entire shapes of the use surfaces 16 of the upper mold 11and the lower mold 12 in the mold 10 is obtained to cope with the error(error of the average surface refractive power) of the spherical shapecomponent in the curved surface of the molded optical lens. Based on thepolynomial component which is the second term of the above-describedequation (1), the local shape correction information for correcting thelocal shapes of the use surfaces 16 of the above-described upper mold 11and the lower mold 12 is obtained to cope with the error of thecomponents other than the spherical shape in the curved surface of themolded optical lens. By obtaining the entire shape correctioninformation and the local shape correction information separately andindependently in this manner, the upper mold 11 and the lower mold 12can be designed by precisely reflecting the errors of the optical lens(the error of the spherical shape component and the error of thecomponents other than the spherical shape) in the correction informationand carrying out suitable correction.

(4) The measured value obtained by measuring the curved shape of themolded optical lens is approximated by the equation (2) which is theequation of the aspherical surface and the curved surface of theabove-described optical lens is specified. Therefore, as compared withthe case where the curved surface of the optical lens is specified byusing the equation (1) which is difficult to handle with a calculator,determination can be carried out by easy calculation, and thecoefficient B_(2i) of the equation (2) can be quickly calculated.Therefore, the correction information corresponding to the deformation(error) of the optical lens is easily calculated, and the upper mold 11and the lower mold 12 of the mold 10 for molding the optical lens in adesired shape can be easily designed.

(5) The marks (not shown) provided at the use surfaces 16 in the uppermold 11 and the lower mold 12 of the mold 10 are transferred onto thecurved surface 31 of the optical lens 30 shown in FIG. 9 and thetransfer mark 32 (vertex transfer mark part 33, the peripheral parttransfer mark parts 34A and 34B) is formed thereon. The transfer mark 32is located at the spot which should be measured in the curved surface 31of the optical lens 30. When the curved shape of the optical lens formedfrom the mold 10 is measured, the shape of the curved surface 31 of theabove-described optical lens 30 is measured as the above-describedtransfer marking 32 located at the spot to be measured as a reference.Thereby, measurement of the curved surface shape of the optical lens 30can be accurately carried out. As a result, the measured value isapproximated by the equation (1) or the equation (2) of the asphericalsurface, the curved surface of the optical lens is specified as theaspherical surface, the correction information is calculated, andthereby, the use surfaces 16 of the upper mold 11 and the lower mold 12in the mold 10 can be precisely designed.

[B] Second Embodiment (FIG. 11, FIG. 12)

(Explanation of Compiling Correction Information into Database)

FIG. 11 is a graph showing a shape change rate curve which is a part ofthe local shape correction information compiled into database that isused in a second embodiment in the method for designing a mold accordingto the present invention. FIG. 12 is a graph showing the entire shapecorrection information which is compiled into database that is used inthe second embodiment in the method for designing the mold according tothe present invention. In the second embodiment, the explanation of thesame parts as in the aforementioned first embodiment will be omitted byusing the same reference numerals and symbols, and the names.

The second embodiment differs from the aforementioned first embodimentin the following point. In FIG. 8, steps S31 to S40 are previouslycarried out for all kinds of molds. On this occasion, each correctioninformation is compiled into database. After creation of the database,steps S35 to S40 are carried out without performing steps S31 to S34.

Namely, in the first embodiment, one kind of optical lens is molded bytests concerning the lens material and the design curved surface shapeof the optical lens, and the correction information (the entire shapecorrection information, the local shape correction information) isobtained. By directly using the correction information, the upper mold11 and the lower mold 12 of the mold 10 are corrected and designed.

On the other hand, in the second embodiment, a number of kinds ofoptical lens differing in the lens material and the design curvedsurface shape of the optical lens as the characteristics of the opticallens are respectively molded by tests in advance, and the correctioninformation obtained at that time is compiled into database for eachcharacteristic of the optical lens. After creation of the database, thedesign values of the use surfaces 16 of the upper mold 11 and the lowermold 12 of the mold 10 for mass production of each of the optical lensesare corrected and designed by using the correction information compiledinto database without another test-molding or by only simple testmolding.

Namely, in the second embodiment, the use surfaces 16 of the upper molds11 and the lower molds 12 of a large number of molds 10 with which moldsrespective plurality of kinds of optical lenses differing in the shapeof the design curved surface are molded are designed with respect toeach of a number of lens materials with different refractive indexes.The optical lenses are molded by tests by using a number of designedmolds 10, and the curved surface shape is measured for each of themolded optical lenses. Then, as in the aforementioned embodiment, theabove-described measured value is approximated by the equation (2) andthe curved surface shape of each of the optical lenses is quantified. Atthis time, the vertex curvature C and the aspherical coefficient A_(2i)(aspherical coefficients A₄, A₆, A₈, A₁₀) are obtained from thecalculated coefficient B_(2i), and the curved surface shape of each ofthe molded optical lenses is quantified and specified by the equation(1).

Then, as in the aforementioned embodiment, data analysis is performedwith respect to each of the curved surface shape of the optical lenseswhich are molded and specified by the equation (1). Then, the entireshape correction information is obtained from the first term (K=0) ofthe equation (1) of each of them, and the shape change rate curve whichis a part of the local shape correction information is obtained from thesecond term of the equation (1) of each of them.

FIG. 11 shows the shape change rate curve of each molded optical lens ineach position from the lens vertex in the optical lens when a pluralityof optical lenses differing in the shape of the design curved surfaceare molded. In this case, the refractive index of the lens material ofthe optical lens is 1.699. In FIG. 11, the horizontal axis represents adistance (mm) from the lens center, and 0 at the central portion of thegraph represents the optical lens center. The vertical axis in FIG. 11represents the shape change rate, and 0% indicates no shape change andno need of correction.

As shown as an example in FIG. 11, the shape change rate curve of themolded optical lens is calculated for each lens material differing inrefractive index and each shape of the design curved surfaces of theoptical lenses, and is compiled into database. Reference symbols a, b,c, d and e in FIG. 11 represent the shape change rate curves when theshapes (radiuses of curvature) of the design curved surfaces of theoptical lenses are respectively the shape corresponding to +2.00 D, theshape corresponding to 0.00 D, the shape corresponding to −2.00 D, theshape corresponding to −6.00 D, and the shape corresponding to −10.00 D.

In FIG. 12, the horizontal axis represents the surface refractive power(D) expressing the lens shape, and numeric value 1 on the horizontalaxis represents the lens shape with a large radius of curvature and asmall curve value, while numeral value 6 on the horizontal axisrepresents the lens shape with a small radius of curvature and a largecurve value. The vertical axis represents the entire shape correctionvalue, and 0 D indicates no shape change and no need of correction.

FIG. 12 shows relationships of the entire shape correction informationof molded optical lenses and the design curved surfaces of the opticallenses by the curve α on the convex surface side and by a curve β on theconcave surface side respectively when a plurality of optical lensesdiffering in the shape of the design curved surface of the optical lensare molded. In this case, the optical lens has the lens material of arefractive index of 1.699, and is a spectacle glass lens in the meniscusshape having the convex surface and the concave surface. As shown as anexample in FIG. 12, the entire shape correction information of themolded optical lens is calculated for each lens material differing inrefractive index, and for each shape of the design curved surface of theoptical lens, and is compiled into database.

Note that in FIG. 11 and FIG. 12, the shapes (radius of curvatures) ofthe design curved surfaces of the optical lenses are shown by beingconverted into surface refractive power (unit: D (diopter)) by using theaforementioned equation (3).

The case of producing the optical lenses in volume with different lensmaterials and different shapes of the design curved surfaces will bedescribed. First, among the shape change rate curves of the opticallenses compiled into database as described above, the shape change ratecurve concerning the optical lens with the same lens material (the samerefractive index) and the same design curved surface shape as theoptical lens to be produced in volume is extracted. Then, the value ofan optional position from the lens vertex of the shape change rate curveis multiplied by the height (Z value) of the design curved surface ofthe optical lens in the corresponding position to calculate the localshape correction information in the position. The local shape correctioninformation is calculated in all the positions of the optical lens. Morespecifically, when the refractive index is 1.669, and the curved surfaceshape corresponds to −6.00 D, the shape change curve d in FIG. 11 isselected. Then, by multiplying the corresponding lens design surfaceheight (Z value), the local correction information is determined in allthe positions in the optical lens. Similarly, when the curved surfaceshape corresponds to −10.00 D, the shape change rate curve e in FIG. 11is selected.

Incidentally, FIG. 11 shows that if the curved surface shape changeseven with the same lens material, the shape change rate curve changesdynamically. Further, the curved surface shape value −2.00 D (curve c inFIG. 11) is smaller in shape change rate than the curved surface shapevalue −6.00 D (curve d in FIG. 11), and the shape change rate and thecurve value of the curvature shape are proportional to each other.However, the curved surface shape value −10.00 D (curve e in FIG. 11) issmaller in shape change rate than the curved surface shape value −2.00 D(curve c in FIG. 11), and they are inversely proportional to each other.Accordingly, it is determined that the shape change of the complicatedshape as a lens expresses a complicated form and it is difficult toperform proper correction with the prior art.

Next, the entire shape correction information concerning the opticallens of the same lens material (the same refractive index) and the samedesign curved shape as the optical lens to be produced in volume isextracted from the entire shape correction information of the opticallens which is compiled into database.

Incidentally, FIG. 12 shows that when the curved shape changes even withthe same lens material, the entire shape correction value also changesirregularly. For example, in the convex surface, the entire shapecorrection value is proportional to the surface refractive power at thesurface refractive power of 0 to 3 D. On the other hand, when thesurface refractive power becomes larger than 4 D, the entire shapecorrection value becomes constant at −0.05 D. Further, on the concavesurface side, the entire shape correction value is constant except atsome surface refractive powers. Accordingly, it turns out that the shapechange of the complicated shape as a lens is unpredictable at presentand it is difficult to perform suitable correction with the prior art.

The use surfaces 16 in the upper mold 11 and the lower mold 12 of themold 10 are designed to be the design curved surfaces of the opticallens to be produced in volume. When the optical lens is produced involume, the local shape correction information calculated based on theshape change rate curve extracted from the database as described aboveand the entire shape correction information which is extracted from thedatabase are added respectively to the design values of theabove-described use surfaces 16 in the Z-direction. Thereby, the designvalues of the use surfaces 16 in the upper mold 11 and the lower mold 12of the mold 10 for molding the optical lens to be produced in volume arecorrected and calculated, and the upper mold 11 and the lower mold 12 ofthe mold 10 are designed.

(Effect of the Second Embodiment)

As constructed as above, the above-described second embodiment alsoprovides the following effect (6) other than the same effects as theeffects (1) to (5) in the aforementioned first embodiment.

(6) The entire shape correction information and the shape change ratecurve which is a part of the local shape correction information are madeto separate and be independent, and are compiled into database for eachlens material and each shape of the design curved surface of the opticallens, and by using each correction information compiled into databaseand the like, the design values of the use surfaces 16 in the upper mold11 and the lower mold 12 of the mold 10 are corrected and designed. As aresult of this, by taking out the entire shape correction informationand the local shape correction information (to be accurate, the shapechange rate curve which is a part of the local shape correctioninformation) which are suitable for the lens material and the shape ofthe design curved surface of the optical lens from the database,correction information and the like of the design values of the usesurfaces 16 in the upper mold 11 and the lower mold 12 of the mold 10can be determined in a short time without carrying out test molding. Asa result, the use surfaces 16 in the upper mold 11 and the lower mold 12of the mold 10 can be efficiently designed.

[C] Third Embodiment

(Explanation of Aspherical Shape Correcting Method by SphericalCorrection Value)

The third embodiment is for correcting and designing design values ofthe use surfaces which are molding surfaces in the upper mold and thelower mold of the mold with which a molded product (optical lens) withthe curved surface in the aspherical shape is molded by utilizing thecorrection information (the entire shape correction information, theshape change rate which is a part of the local shape correctioninformation) which is compiled into database in the aforementionedsecond embodiment and for molding a molded product (optical lens) withthe curved surface in a spherical shape.

The method for compiling the entire shape correction information formolding the optical lens with the curved surface in a spherical shape,and the shape change rate which is a part of the local shape correctioninformation into database for each characteristic of the optical lenswith the design curved surface having a spherical shape is the same asthe aforesaid second embodiment, and the explanation of the method willbe omitted. Here, the characteristics of the above-described opticallens are the lens material of the optical lens with the curved surfacein the spherical shape, and the shape of the design curved surfacehaving the spherical shape.

Design of the use surfaces in the upper mold and the lower mold of themold for molding the optical lens with the curved surface in anaspherical shape starts first with extraction of the entire shapecorrection information and the shape change rate which is a part of thelocal shape correction information which are compiled into database andsuitable for the optical lens having the aspherical shape.

Namely, the entire shape correction information and the shape changerate that is a part of the local shape correction information, which arecompiled into database, about the optical lens which is of the same lensmaterial as the optical lens with the curved surface in the asphericalshape to be molded and includes the design curved surface of thespherical shape having the radius of curvature corresponding to theradius of curvature at the vertex or the average radius of curvature inthe design curved surface of the aspherical shape of the optical lensare extracted from the database. Here, the above-described radius ofcurvature at the vertex means, for example, the radius of curvature atthe vertex in the design curved surface of the aspherical shape of theoptical lens to be molded. The above-described average radius ofcurvature means the average radius of curvature in the entire surface ofthe lens in the design curved surface of the aspherical shape of theoptical lens to be molded.

(Aspherical Shape Correcting Method by Spherical Correction Value:Correction Value Calculation from Database)

For example, the case where the radius of curvature at the vertex of thedesign curved surface of the optical lens with the curved surface to bemolded is in an aspherical shape is +2.00 D (diopter) is considered.First, with respect to the optical lens which is of the same lensmaterial as the optical lens to be molded and including the designcurved surface of the spherical shape having the radius of curvaturecorresponding to the above-described radius of curvature at the vertex,the corresponding database is referred to. On the convex surface side,at 2 D of “refractive power expressing the convex surface side lensshape” on the horizontal axis, the corresponding entire shape correctionvalue of −0.100 D on the curve α is taken out as the entire shapecorrection information from the entire shape correction informationshown in, for example, FIG. 12. Meanwhile, on the concave surface side,at 2 D of “refractive power expressing the concave surface side lensshape” on the horizontal axis, the corresponding entire shape correctionvalue of −0.125 D on the curve β is extracted. Similarly, from the shapechange rate which is a part of the local shape correction informationshown in, for example, FIG. 11 compiled into database, the curve a istaken out as the shape change rate.

Next, the value at an optional position from the lens vertex at theextracted shape change rate is multiplied by the height (Z value) of thedesign 5 curved surface of the aspherical shape of the optical lens atthe corresponding position, and thereby, the local shape correctioninformation at the position is calculated. Then, the local shapecorrection information is calculated at all the positions of the opticallens with the curved surface in the aspherical shape.

(Aspherical Shape Correcting Method by Spherical Surface CorrectionValue: Method for Adding Correction Value)

Next, the local shape correction information calculated based on theshape change rate extracted from the database as described above, andthe entire shape correction information extracted from the database areadded in the Z-direction to the design values of the use surfaces in theupper mold and the lower mold of the mold, which are designed to be thedesign curved surface of the aspherical shape of the optical lens to bemolded.

As for the local shape correction information, for example, the localshape correction information calculated at each position of the opticallens of which curved surface is in the aspherical shape is added in theZ-direction to the design value at each position in the use surfaces ofthe above-described upper mold and lower mold designed to be the designcurved surface of the aspherical shape. As for the entire shapecorrection information, the entire shape correction informationextracted from the database is added in the Z-direction to, for example,the design values at the vertexes in the use surfaces of theabove-described upper mold and lower mold, which are designed to be thedesign values of the aspherical shape.

As described above, the design values of the use surfaces in the uppermold and the lower mold of the mold for molding the optical lens ofwhich curved surfaces are in the aspherical shape are corrected andcalculated, and the upper mold and the lower mold of the mold aredesigned.

(Effect of the Third Embodiment)

Since it is constructed as above, the above-described third embodimentprovides the following effect (7) in addition to the effects (1) to (5)of the aforesaid first embodiment.

(7) Information corresponding to an error of the curved surface of theabove-described optical lens specified by the equation of the asphericalsurface and the design curved surface of the spherical shape of theoptical lens is compiled into database for each characteristic of theoptical lens as the correction information for molding the optical lensof which curved surface are in spherical shape. Then, by using thecorrection information compiled into the database, the design values ofthe use surfaces in the upper mold and the lower mold of the mold formolding the optical lens of which curved surfaces are in the asphericalshapes are corrected and designed. As a result of this, by extractingthe correction information suitable for the optical lens having thecurved surfaces in the aspherical shapes from the database, thecorrection information for correcting the design values of the usesurfaces in the upper mold and the lower mold of the mold for moldingthe optical lens of which curved surfaces are in the aspherical shapescan be determined in a short time. As a result, the use surfaces in theupper mold and the lower mold of the mold for molding the optical lensin a desired shape, of which curved surfaces are aspherical surfaces canbe efficiently designed.

[D] Fourth Embodiment (FIG. 13, FIG. 14)

(Explanation of Designing Method of Non-Molded Surface)

A fourth embodiment relates to a designing method of a mold in the caseof polymerization molding of a plastic lens by using a mold made ofglass or ceramics.

Conventionally, for polymerization molding of a plastic lens forspectacle glasses, a mold (also called a molding die) in which a set ofupper mold and a lower mold (also called an upper die mold and a lowerdie mold respectively) made of glass or ceramics are held at apredetermined space by an annular gasket is used. A plastic monomer ischarged into the mold and heated and polymerized, and thereby, a plasticlens in a desired shape is obtained.

In the lower mold in this case, an upper surface is formed as a lenstransfer surface in a convex surface shape, while a lower surface formedas a non-transfer surface in a concave surface shape, and an outerperipheral part is formed as a cylindrical surface (for example, seeJapanese Patent Application Laid-open No. 4-232706). The lens transfersurface is for molding a rear surface (concave surface) of the lens, andtherefore, it is specified as a convex curved surface in accordance withthe lens design value. On the other hand, the non-transfer surface isthe surface which is not used for molding, and therefore, it isgenerally formed as a concave spherical surface with a proper curvaturewhich satisfies the specifications such as a height dimension of thecylindrical surface (edge thickness).

When producing such a mold, it is usually produced by grinding/polishingblanks of glass of a specified size which is molded in advance.Especially for polishing the concave spherical surface of thenon-transfer surface, a polishing tool (polishing plate) is used.Incidentally, the curvature of the non-transfer surface is changed foreach mold conventionally, and therefore, a different polishing tool isused for each curvature to be obtained by polishing in the existingstate.

As described above, the curvature of the non-transfer surface (concavespherical surface) is conventionally changed for each mold as describedabove, and thereby, it is necessary to use a different polishing toolfor each curvature to be obtained by polishing. Therefore, the kind ofpolishing tools increases, and there is a problem of increasing cost.

In view of the above-described circumstances, the fourth embodiment hasits object to provide a method for designing a mold for a plastic lenswhich is capable of achieve cost down by decreasing the kind ofpolishing tools which polishes non-transfer surfaces.

A first construction in the fourth embodiment specifies outer surfaceshapes of the molds in the lens transfer surfaces, non-transfersurfaces, outer peripheral cylindrical surfaces and flat surfaces whendesigning a plurality of kinds of molds differing in size. Theabove-described lens transfer surface is a part of a mold which iscomposed of a convex curved surface formed to be circular in plane viewwith an optical axis of the mold as a center. The above-describednon-transfer surface is on a back surface side of the lens transfersurface, and is a part of the mold composed of a concave sphericalsurface formed to be circular in plane view with the above-describedsame optical axis as the center. The above-described peripheralcylindrical surface is a part of the mold which is formed from an outercircumferential edge of the lens transfer surface to the back surfaceside with the above-described optical axis as the center. Theabove-described flat surface is a part of the mold which is formed to beannular at an outer peripheral side of the non-transfer surface, withits own inner peripheral edge intersecting the outer peripheral edge ofthe non-transfer surface, and with an outer peripheral edge intersectingan end edge of the outer peripheral cylindrical surface. Then, the curveof the lens transfer surface, a wall thickness on the above-describedoptical axis between the lens transfer surface and the non-transfersurface, and the height of the outer peripheral cylindrical surface arerespectively set based on the design data. Further, the width of theannular flat surface is adjusted to correspond to the shape of theblanks of the minimum size from which the mold can be worked to be takenout. In this manner, the curvature of the non-transfer surface composedof the concave spherical surface in each of the molds is made constant.

A second construction in the fourth embodiment is characterized byadjusting the width of the annular flat surface to be 4 mm to 6 mm, inthe above-described first construction.

According to the fourth embodiment, the curvature of the concavespherical surface of the non-transfer surface is made constant byadjusting the width of the annular flat surface, and therefore, the kindof polishing tools which polish concave spherical surfaces can bedecreased, which results in reduction of working cost of molds.

Hereinafter, the fourth embodiment will be further described withreference to the drawings.

FIG. 13 is a sectional view of a mold for molding a plastic lens. Themold is composed of a lower mold 1, an upper mold 2 and a cylindricalgasket 3, and a cavity 4 of which periphery is surrounded by the gasket3 is formed between the lower mold 1 and the upper mold 2. Accordingly,by charging a monomer into the cavity 4 and polymerizing it, a plasticlens can be molded.

The outer surface shape of the lower mold 1 in this case is defined by alens transfer surface 1A, a non-transfer surface 1B, an outer peripheralcylindrical surface 1C and a flat surface 1D. The lens transfer surface1A is a part of the lower mold 1, which is composed of a convex curvedsurface formed to be circular in plane view with an optical axis L(center axis) as a center. The non-transfer surface 1B is a part of thelower mold 1, which is composed of a concave spherical surface formed ona back surface side of the lens transfer surface 1A to be circular inplane view with the same optical axis L as a center. Further, the outerperipheral cylindrical surface 1C is a part of the lower mold 1, whichis formed from an outer circumferential edge of the transfer surface 1Awith the optical axis L as a center to the back surface side. The flatsurface 1D is a part of the lower mold 1, which is formed into anannular shape at an outer peripheral side of the non-transfer surface1B, with its own inner peripheral edge intersecting an outer peripheraledge of the non-transfer surface 1B, and its outer peripheral edgeintersecting an end edge of the outer peripheral cylindrical surface 1C.

In this case, a curve of the transfer surface 1A, a wall thickness SS1on the optical axis L between the transfer surface 1A and thenon-transfer surface 1B, and a height SS2 of the outer peripheralcylindrical surface 1C (edge thickness or rim thickness) arerespectively set as fixed values based on the design data of the lens. Acurvature SS3 of the non-transfer surface 1B and a width SS4 of theannular flat surface 1D are set to the values which can be optionallychanged as long as they satisfy the above-described fixed values.

Next, a method for designing the lower mold 1 will be explained.

As shown in FIG. 14, there are the following five elements fordetermining the shape of the lower mold 1 of the above-described type.

(1) Curve of the transfer surface 1A

(2) Wall thickness SS1

(3) Height SS2 of the outer peripheral cylindrical surface 1C

(4) Curvature SS3 of the non-transference surface 1B

(5) Width SS4 of the annular flat surface 1D

Among them, (1) curve of the transference surface 1A, (2) wall thicknessSS1 and (3) height SS2 of the outer peripheral cylindrical surface 1Ccan be fixedly set based on the lens design data, but (4) curvature SS3of the non-transference surface 1B and (5) width SS4 of the annular flatsurface 1D can be optionally changed.

Thus, in the designing method of this embodiment, a blank 5 of theminimum size which can realize (1) curve of the transfer surface 1A, (2)wall thickness SS1 and (3) height SS2 of the outer peripheralcylindrical surface 1C is selected first while (4) curvature SS3 of thenon-transfer surface 1B and (5) width SS4 of the annular flat surface 1Dare optionally adjusted. Then, the width SS4 of the annular flat surface1D is adjusted corresponding to the shape of the blank 5, and thereby,the curvature SS3 of the non-transfer surface 1B composed of a concavespherical surface in each mold is made constant.

As described above, the curvatures SS3 of the non-transfer surfaces 1Bare made constant in a plurality of kinds of molds, and the non-transfersurfaces 1B are formed into the same spherical shape, whereby thepolishing tool used in a polishing process of the non-transfer surface1B can be used in common. Accordingly, the production cost of molds canbe reduced. In this case, the width SS4 of the annular flat part 1D isset in the range of 4 mm to 6 mm, and is preferably processed within thelimits of the size of the blank 5.

Consequently, according to the fourth embodiment, the following effect(14) is provided.

(14) Since the curvature SS3 of the concave spherical surface of thenon-transfer surface 1B is made constant by adjusting the width SS4 ofthe annular flat surface 1D, the kind of polishing tools for polishingthe concave spherical surface can be reduced, and thereby the processingcost of the mold 10 can be reduced.

INDUSTRIAL AVAILABILITY

The present invention is described based on the above-described eachembodiment thus far, but the present invention is not limited to this.

For example, in the embodiments, the optical lens is manufactured bybeing molded by using the cast method, but the present invention can bealso applied to the case where the optical lens is manufacturedaccording to the manufacturing method other than the cast method. Inconcrete, in the case where the plastic lens is directly cut andpolished, the present invention can be applied to cut surface shape datacorrection in a grinding process, the shape correction and therefractive power correction of the polishing tool (polishing plate) in apolishing process. Further, the present invention is applicable tocorrection or the like of a slumping mold.

Besides, the case where the mold is glass is described in theabove-described embodiments, but the present invention can be applied toother molds with a high thermal shrinkage factor, for example, in thecase of molding by a metal mold.

In the above-described embodiments, the case where the optical lens ofwhich surface is in a spherical shape is described as the test moldedproduct. However, an optical lens of which surface is in an asphericalshape can be applied as the test molded product.

Further, in the above-described embodiment, the case of the optical lensof which surface is in a spherical shape and is rotationallysymmetrical, or the optical lens of which surface is in an asphericalshape is described as a finished molded product, but the optical lenseshaving a toric surface, an atoric surface and the like can be made asfinished molded products. Here, the toric surface means the surfacewhich has two principal meridians orthogonal to each other, with eachprincipal meridians constructed by a spherical shape. The atoric surfacemeans the surface with each of its principal meridians constructed by anaspherical shape.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a sectional side view showing a mold having an upper mold anda lower mold which are produced by carrying out a first embodiment in amethod for designing a mold according to the present invention;

FIG. 2 is a sectional side view showing the lower mold in FIG. 1;

FIG. 3 is a flowchart showing a production procedure of an optical lens(plastic lens) using the mold in FIG. 1;

FIG. 4 is a flowchart showing a production procedure of the upper moldand the lower mold in FIG. 1;

FIG. 5 is a graph showing a molded curved surface 21, a design curvedsurface 20 and the like of the optical lens which is a molded productmolded by tests from the mold in FIG. 1;

FIG. 6 is a graph showing a deviation amount by which a polynomialcomponent of the molded curved surface 21 of the optical lens, which ismolded by tests and specified by the equation (1), deviates with respectto the reference spherical surface component (curved surface shape 22)in FIG. 5;

FIG. 7 is a schematic diagram showing calculation and the like of entireshape correction information and local shape correction information in adesign process of the upper mold and the lower mold in FIG. 1;

FIG. 8 is a flowchart concretely showing a design procedure of the uppermold and the lower mold in FIG. 1;

FIG. 9(A) is a front view showing a transfer marking which istransferred from the mold in FIG. 1 and formed on a curved surface ofthe optical lens, FIG. 9(B) is a partially enlarged view showing avertex transfer marking of FIG. 9(A), and FIG. 9(C) is a partiallyenlarged view showing a peripheral edge part transfer marking in FIG.9(A);

FIG. 10 shows a shape error which the molded curved surface of theoptical lens that is the molded product has with respect to the designcurved surface at each position of the optical lens, FIG. 10(A) is agraph in the case of the optical lens molded by using the mold designedby the method for designing the mold in the first embodiment, and FIG.10(B) is a graph in the case of the optical lens molded by the moldwhich is designed by making correction by using an average curvature ina first prior art;

FIG. 11 is a graph showing a shape change rate that is a part of thelocal shape correction information compiled into database, which is usedin a second embodiment in the method for designing a mold according tothe present invention;

FIG. 12 is a graph showing the entire shape correction information thatis compiled into database, which is used in the second embodiment in themethod for designing the mold according to the present invention;

FIG. 13 is a sectional view of an assembled state of a mold designed bya fourth embodiment of the method for designing a mold according to thepresent invention; and

FIG. 14 is a view showing relationship between the size of the lowermold and blanks in the explanatory view of the method for designing amold in the fourth embodiment.

EXPLANATION FOR REFERENCES

10 A mold

11 A upper mold

12 A lower mold

16 use surfaces (a molded surface)

20 A designed curved surface

21 A molded curved surface

22, 23 A curved shape

30 An optical lens

31 A curved surface

32 A transfer mark

33 A vertex transfer mark part

34A, 34B peripheral part transfer mark parts

A_(2i) A aspherical coefficient

B_(2i) A coefficient

C A vertex curvature

R₀ A design radius of curvature at the vertex

R A radius of curvature at the vertex

O A vertex

P An optical axis

1. (canceled)
 2. A method for designing a mold, comprising: preparing amold of which molding surface is formed to be a design curved surface ofa molded product; measuring a curved surface shape of a molded productwhich is molded from the mold, and specifying a curved surface of theabove-described molded product by approximating a measured value by anequation of an aspherical surface; comparing the specified curvedsurface of the above-described molded product and the design curvedsurface of the above-described molded product to obtain an error of boththe curved surfaces; and correcting the above-described molded surfaceof the above-described mold by using information corresponding to theerror as correction information to design it, wherein said correctioninformation includes entire shape correction information correcting anentire shape of the molding surface of the mold to cope with an error ofa spherical shape component in the curved surface of the molded product,and local shape correction information correcting a local shape of theabove-described molding surface of the above-described mold to cope withan error of a component other than the spherical shape in the curvedsurface of the molded product, said entire shape correction informationand said local shape correction information are independentlycalculated, and the shape of said molded surface of said mold iscorrected by using said entire shape correction information and saidlocal shape correction information.
 3. The method for designing a moldaccording to claim 2, wherein the above-described equation of theaspherical surface is a polynomial including a spherical shape componentin the curved surface of the molded product and a component other thanthe spherical shape in the curved surface of the molded product.
 4. Themethod for designing a mold according to claim 2, wherein theabove-described equation of the aspherical surface adds a sphericalshape component in the curved surface of the molded product and acomponent other than the spherical shape in the curved surface of themolded product.
 5. The method for designing a mold according to claim 2,wherein the above-described equation of the aspherical surface is thefollowing equation: $\begin{matrix}{Z = {\frac{C\quad\rho^{2}}{1 + \sqrt{1 - {( {1 + K} )C^{2}\rho^{2}}}} + {\sum\limits_{i = 2}^{m}{A_{2i}\rho^{2i}}}}} & (1)\end{matrix}$ where Z is a distance measured from a vertex of the moldedproduct in an axial direction of the molded product, p satisfiesp²=X²+Y² when X and Y are distances measured in a perpendiculardirection to the above-described axis from the above-described vertex, avertex curvature C satisfies C=1I/R when R is set as a radius ofcurvature at the vertex, K is a conic coefficient, and A₂₁ is anaspherical coefficient (i is an integer).
 6. The method for designing amold according to claim 5, wherein in the above-described asphericalcoefficient A₂₁, i is 2 to
 5. 7. The method for designing a moldaccording to claim 5, further comprising: obtaining the entire shapecorrection information correcting the entire shape of the moldingsurface of the mold to cope with the error of the spherical shapecomponent in the curved surface of the molded product, according to areference spherical component which is a first term (K=O) of theabove-described equation (1); and obtaining the local shape correctioninformation correcting a local shape of the above-described moldingsurface of the above-described mold to cope with the error of acomponent other than the spherical shape in the curved surface of themolded product, according to a polynomial component which is a secondterm of the above-described equation (1).
 8. The method for designing amold according to claim 7, wherein the entire shape correctioninformation in the molding surface of the above-described mold isdetermined based on a difference between a radius of curvature of areference spherical surface expressed by the reference spherical surfacecomponent which is the first term (K=0) of the equation (1) and anaverage radius of curvature in the entire design curved surface of themolded product or a radius of curvature in a vertex refractive power. 9.The method for designing a mold according to claim 7, wherein the localshape correction information in the molding surface of theabove-described mold is determined based on a shape change rate which isexpressed by the polynomial component that is the second term of theequation (1) and is calculated by using a height (Z value) of acomponent other than the spherical shape in the curved surface of themolded product, and a height (Z value) of the design curved surface ofthe above-described molded product.
 10. The method for designing a moldaccording to claim 7, wherein a design of the molding surface of theabove-described mold is made by adding the entire shape correctioninformation and the local shape correction information to the designcurved surface of the molded product.
 11. The method for designing amold according to claim 2, wherein the above-described equation of theaspherical surface is the following equation: $\begin{matrix}{Z = {\sum\limits_{i = 1}^{m}{B_{2i}\rho^{2i}}}} & (2)\end{matrix}$ which is obtained by transforming the following equation.$\begin{matrix}{Z = {\frac{C\quad\rho^{2}}{1 + \sqrt{1 - {( {1 + K} )C^{2}\rho^{2}}}} + {\sum\limits_{i = 2}^{m}{A_{2i}\rho^{2i}}}}} & (1)\end{matrix}$
 12. The method for designing a mold according to claim 11,further comprising: obtaining the vertex curvature C and an asphericalcoefficient AA of the equation (1) from a coefficient B₂₁ of theabove-described equation (2), and determining the curved surface of themolded product by the equation (1); obtaining the entire shapecorrection information correcting the entire shape of the moldingsurface of the mold to cope with an error of the spherical shapecomponent in the curved surface of the molded product, according to thereference spherical component which is the first term (K=O) of theequation (1); and obtaining the local shape correction informationcorrecting the local shape of the above-described molding surface of theabove-described mold to cope with the error of a component other thanthe spherical shape in the curved surface of the molded product,according to the polynomial component that is the second term of theabove-described equation (1).
 13. The method for designing a moldaccording to claim 2, wherein measurement of the curved surface shape ofthe above-described molded product comprises: preparing a mold with acurved surface measuring mark provided on the molding surface; andmeasuring the curved surface shape of the molded product molded from themold, and on this occasion, measuring the above-described curved surfaceshape with a transfer mark, which is formed by the above-described markbeing transferred onto the curved surface of the molded product, and islocated at an arbitrary spot to be measured, as a reference.
 14. Themethod for designing a mold according to claim 13, wherein theabove-described transfer mark has a vertex transfer mark part formed ata vertex of the curved surface of the molded product, and edge parttransfer mark parts formed at positions which are point-symmetrical withrespect to the above-described vertex at edge parts of theabove-described curved surface, and measures the above-described curvedsurface of the above-described molded product by passing the vertextransfer mark part and the edge part transfer mark parts.
 15. The methodfor designing the mold according to claim 14, wherein a pair of or aplurality of pairs of the above-described edge part transfer mark partsare formed at positions which are point-symmetrical with respect to thevertex of the curved surface of the molded product.
 16. The method fordesigning a mold according to claim 2, wherein the above-describedmolded product is an optical lens of which curved surface is in aspherical shape or an aspherical shape.
 17. The mold which is formed bycarrying out the method for designing a mold according to claim
 2. 18.The molded product which is formed by using the mold according to claim17.
 19. The molded product according to claim 18, wherein the moldedproduct is a spectacle lens in a meniscus shape.
 20. The molded productaccording to claim 19, wherein the molded product is a spectacle lenssymmetrical with respect to a center.